We plan to continue our studies on the properties and function of the rabbit liver microsomal cytochrome P-450-containing hydroxylation system. A major goal of the work is to obtain all of the enzyme components in homogeneous state. P-450 LM2 and LM4 are already pure and will now be characterized by sequencing and other techniques. Attempts will be made to purify the other four forms of rabbit liver microsomal cytochrome P-450 not yet obtained in an electrophoretically homogeneous state; to investigate the interactions of purified cytochrome P-450, purified NADPH-cytochrome P-450 reductase, and phosphatidylcholine; and to determine the substrate specificity of the individual forms of the cytochrome in the reconstituted enzyme system. In collaboration with others, the position-specific oxygenation of benzo(a)pyrene by different forms of purified cytochrome P-450 will be determined. BIBLIOGRAPHIC REFERENCES: Liver Microsomal NADPH-Cytochrome P-450 Reductase: Electron Accepting Properties Vermilion, J. L., and Coon, M. J. (1977) Fed. Proc. 36, in press. Properties of Two Highly Purified Forms of Liver Microsomal Cytochrome P-450, Vatsis, K. P., Chiang, Y. C., and Coon, M. J. (1977) Fed. Proc., in press.